Integrated Modeling of In-Lieu Groundwater Recharge Using Recycled Water for Agriculture-Maximizing Benefits to Groundwater Dependent Ecosystems and Sustainable Groundwater Management
Sacramento Regional County Sanitation District (Regional San)
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The Sacramento Regional County Sanitation District (Regional San) is planning to distribute tertiary treated recycled water to south Sacramento County, which overlies the South American Subbasin, a high-priority basin under the Sustainable Groundwater Management Act. Recycled water will be used by farms in lieu of pumping existing groundwater supplies. The project will result in multiple benefits such as increasing groundwater levels, and improving conditions for adjacent Groundwater Dependent Ecosystems (GDEs) within the Cosumnes River Preserve, increasing in-stream flows for fisheries and improving water supply sustainability. The South Sacramento County Agriculture and Habitat Lands Recycled Water Program proposes reuse of up to 50,000 AFY of recycled water on approximately 16,000 acres. Title 22 recycled water will be produced by the Sacramento Regional Wastewater Treatment Plant through the EchoWater project, a $2 billion dollar wastewater treatment plant upgrade. The SacIWRM model shared by all users in the basin evaluated the water budget for multiple scenarios, all involving delivery of recycled water for agricultural uses in-lieu of groundwater pumping. Regional San partnered with The Nature Conservancy (Conservancy), modeling multiple potential scenarios for recycled water distribution and banking, prioritizing benefits for adjacent habitats, under certain groundwater use conditions. Results project groundwater levels increasing as much as 30’, with elevation increases extending outside the project limits to support valley oak riparian forest health. Raised levels would also benefit wetlands with listed species and increase in-stream flows for anadromous fisheries. Inclusion of ecosystem benefits in the design of the project provides a model for multi-benefit water supply projects. It also informs how groundwater basins can best identify, protect and even improve Groundwater Dependent Ecosystems with Sustainable Groundwater Management Act implementation. Some supplied water goes to Stone Lakes National Wildlife refuge, a wetland area in the Pacific flyway, benefitting migratory waterfowl and other birds. In another area, a recharge component is being evaluated. It would use winter over-irrigation to create flooded habitat for migratory bird roosting and foraging, while allowing continued farming during the primary growing season. Siting of the recharge farm on looser soils increases project benefits for the water table and instream flows in the Cosumnes River. 293,000 AF of new groundwater storage is projected over 30 years of project operation, with twice that amount returning to area rivers. The presentation will include maps showing groundwater elevation and in-stream flow benefits, some arriving less than ten years after project implementation. One scenario modeled includes hypothetical extraction of groundwater by municipal users in the driest 30% of years. Modeling of this scenario still shows an overall increase in the water table while allowing for improved regional and statewide water storage options and operational flexibility. Assurances for agricultural and environmental users will need to be developed over the next several years to ensure projected benefits occur when implemented, with resulting sustainable groundwater management benefiting both people and nature.